Purpose: The aim of this study was to determine the expression and localization of integrin alpha5beta1 in human retinal pigment epithelium (RPE) and its ability to modulate RPE cell attachment, proliferation, migration, and F-actin cytoskeleton distribution.
Methods: Expression and localization of alpha5beta1 were analyzed on human RPE by immunoblot/immunofluorescence. Polarized secretion of fibronectin was measured. RPE attachments to different substrates were determined using cell attachment screening kits. BrdU incorporation and wound-healing assays were used to test hfRPE proliferation and migration. F-actin cytoskeleton was visualized with phalloidin.
Results: Integrin alpha5beta1 was detected in native adult and fetal human RPE. The alpha5-subunit is predominantly localized at the apical membrane of hfRPE, whereas the beta1-subunit is uniformly detected at the apical/basolateral membranes. The authors also found that hfRPE cultures secrete significant amounts of fibronectin to the apical bath. JSM6427, a specific integrin alpha5beta1 antagonist, significantly inhibited hfRPE cell attachment to fibronectin, but not laminin, or collagen I or IV. JSM6427 also showed a strong inhibitory effect on bFGF, PDGF-BB, and serum-induced cell migration and proliferation. Furthermore, JSM6427 induced significant disruption of the F-actin cytoskeleton of dividing RPE cells but had no effect on quiescent cells.
Conclusions: The apical localization of alpha5beta1 and the secretion of fibronectin to the apical bath suggest the presence of an autocrine loop that can guide the migration of RPE. The strong inhibitory effects of JSM6427 on human RPE cell attachment, proliferation, and migration is probably mediated by F-actin cytoskeletal disruption in proliferating cells and suggests a potential clinical use of this compound in proliferative retinopathies.